Electron-discharge apparatus and method of operating the same.



W. D. COOLIDGE.

ELECTRON DISCl-I ARGE APPARATUS AND METHOD OF OPERATING THE SAME.

APPLICATION FILED MAR. 30. 1915. I

1,211,376; Pafented Jan. 2,1917.

an apparatus for carryin D. COOLING-E, OF S CHENECTADY, NEW YORK, ASSIGNOR TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YOBK.

EIECTEON-DISGHABGE APPARATUS AND METHOD OF OPERATING THE SAME.

To all whom it may concern:

Be it knownthat I, WILLIAM D. Coomncn, a citizenof the United States, residingat Schenectady, in the county of Schenectady,

State of New York, have invented certain new and useful lmprovementsin Electron- Discharge Apparatus and Methods of Opcrating the Same, of which the following is a specification.

The present invention comprises a method of controlling an electron discharge energized bya periodically varying voltage and out this method.

My invention is particu arly applicable to the operation of an X-ray device with a current of variable voltage when it is desired to select a certain part of the current wave and thus, for example, to secure rays of trostatic field is established radially about the cathode in synchronism with the periodicity of the impressed voltage, this field having an electrostatic char e over an un'-' desired range of voltage va ues suitable in polarity an potential to reduce or even entirely suppress the electron discharge. During the intervals that current flow is desired,

for example, near the voltage peaks of each current wave, the intensity and if desired, also the polarity of the field, is changed to promote the electron-discharge.

In the specific embodiment of my invention illustrated diagrammatically an X-ray" tube operated with. a periodically varying current is provided, at the cathode, with means for establishing a ne ativefi'eldover a part of the wave interva and a positive field over another part in synchronism with the supply current.

Referring to the drawing, the X-ray tube 1 is connected to the secondary of a high potential transformer 2 by means of conductors 3, 3'. The'ca'thode 4 consists of a flat spiral filament which is shown on edge. The heating current from a battery 5 is supplied by conductors 6, 6' sealed into the lass stem 7 'in the manner well understood m-the construction of incandescent lamps; The temperature of the filament and thereby the resistance of the tube may be varied by adjusting the resistanceS in the heating circu1t. The anode 9 consists preferably of ductile tungsten. It is attached to a tube 10 consisting of'molybdenum or iron, which Specification of Letters Patent.

Application filed March 80, 1915. Serial No. 18,138.

Patented Jan. 2, 1917.

is held Within asocket 11 forming part of tween the cathode and the anode can occur substantially independently of gas ionization, the anode being deprived of gas by the cathode discharge during the evacuation of the tube.

Surroundingthe cathode 4 is a conductive ring 12 consisting, for example, of iron or molybdenum, and supported by a wire 12 sealed into the stem 7 This ring serves to establish an electrostatic field radially about the cathode in order to control the electron discharge passing betwen the heated cathode and the anode when a suitable potential is impressed across these electrodes. 'When this focusing ring 12 is allowed to assume the potential of the cathode, or a negative potential not materially higher than the potential of the cathode the radial negative field has the effect of concentrating or focusing the electron discharge. upon the .spot of limited area .on the face of the anode. When, however, the negative field is sufiiciently high, the particular value depending, on the potential between the cathode and the anode, the electrons are prevented from leaving the neighborhood of the oathode and a discharge across the vacuous space is prevented entirely. When the electrostatic field of the focusing ring is positive, the passage of the electrons from the oathode to the anode is assisted and the conductivity of the tube is thereby increased. If the electrostatic charge of the focusing ring is change'din a positive direction, that is, even ifit is only made less negative, the resistance of. the tube is decreased.

At the beginning of each halfwave of current, when the impressed voltage is low, the X-rays produced by the cathodedischarge-impinging on the anode are of .low penetrating power, or, as technically termed,

age approaches its maximum, the hardness of the rays increases. The soft rays in some cases are not desired and the cathode discharge over the lower voltage range consumes energy and thereby heats theanode. Q

As the capacity of the tube is limited by the heat storage and the heat-dissipating ca: paclty of the anode, the output of the harder rays may be increased by reducing the production of the soft rays. In the device shown in the drawing, the .ring 12 is suitably charged over desired intervals through conductors 13, 14, for example, by being connected to the terminals of a battery 15,

In series with the conductors 13, 14,.1s a commutator consisting of two disks 17, 18, which connect a source of electromotive force, for example; the battery 15, to the focusing ring so as to make the ring negatlve over a range of impressed voltage at the beginning of a half wave impulse, then pos tive over a range of current near the mainmum voltage, and finally again negative as the impressed voltage drops to zero. These changes in connection are produced synchronously with the variation of the supply volt age by a synchronous motor 19 connected by means of conductors 20 to the same source of energy to which the supply conductors 22 of the transformer 2" are connected. The -commutator disk 17 contains an insulatlng segment 24 of relatively great angular width, and the conductive segments 25, 26, of small angular width. The commutator 18 contains an insulating segment 27 having -two peripheral sectlons substantlally equal in angular width to the conductive segments 25, 26. The conductive segments 28, 29 have an angular width substantially equal to the exposed sections of the insulating segments 24 of the commutator disk 17. These disks are so arranged on the common shaft that the battery will be connected through elther one or the other disk between the focusmg ring 12 and the cathode 4. vFor example, as

illustrated, the positive side of the battery is connected to the focusing ring through the conductors 13, the brushes 36 and the conductor 33. The negative terminal of the battery is connected through the brushes 37, and the conductors 14 and 3' to the cathode 4 of the X-ray tube. When the brushes 36 and 37 have left the conductive segments and pass on to the insulating segments of the commutator disk 17, the brushes 31 and 34 of the commutator disk 1.8 will have traveled to the conductive segments of this commutator disk thereby reversing the potential of the focus-' ing ring 12. It will be noted that in this manner the potential of the focusing ring is made positive during the interval that the passage of current through the X-ray tube is desired, and negative when the passage of current is to be suppressed. The size of the commutators and the distance between the brushes may be varied as desired.

at I claim as new and desire to secure by Letters Patent of the United States, is

- 1. The rocess of selectively opeI ating an electron dlscharge device fed with an energy supply periodlcally varying in voltage which over a range of voltages near the maximum value to increase the cathode discharge and thereby to increase the generation of X-rays.

3'. The process of operating an electron discharge device which consists in supplying said device with a current periodically varying in potential and in synchronism-with the variations of applied potential applying an electrostatic field about the cathode overseleeted portions of the supply current waves to increase the conductivity of said device relative to the remaining portions.

4. The process of operating with a periodically varying current an electrical discharge device having an electron-emitting cathode, an anode' and an inclosing bulb evacuated to'a pressure so low that evidences of positiveionization are substantially absent during the operation of the device, which con- 4 sists in establishing an electrostatic field radially about the cathode, said field having negative potential high enough during intervals when no purrent is desired to prevent the discharge between the cathode and the anode, and periodically reducing the value of said field to or beyond zero during intervals' when current flow is desired.

5; The combination of an electron discharge device comprising coiiperating electrodes and a conductive member surrounding at least in partthe discharge path between said electrodes, a sourceof variable curren connectedto the electrodes of said tube, a source of electromotive force, means for connecting said source between the cathode and the conductive member during selected portions of each wave of sup lycurrent synchronously with the perio current.

city of supply 6. An X-ray apparatus comprising an I 7. An X-ray apparatus comprisingan X- ray tube having an incandescent cathode, a

I source of alternating current, means for establishing a negative static field radially about the cathode over a range of current values when the potential is near the minimum value and means for reversin the polarity of the field near the maximum value of the voltage.

8. The combination of an X-ray tube in the operation of which evidences of positive ionization are substantially absent, a source of electric energy supply therefor of vari-' able voltage, a conductor surrounding in part at least an axis passing through the cathode and the anode of said device and means operating in 'synchronism with the source of energy supply for charging said conductor negative over a "range of current near the minimum value of potential and positive over arange of current value near the maximum value of. potential.

9. The process of selecting predetermined current intervals of an electron dischar e which consists in apply- 

